A real time clock assembly includes paired crystal oscillators that experience changes in frequency responsive to temperature. The differences in frequency changes between the paired crystal oscillators are utilized to determine a temperature utilized to compensate for those shifts in frequency. The predictability of frequency responsive to temperature variations by the paired crystal oscillators is utilized for the determination of temperature.
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5. A real time clock assembly comprising:
a first microcontroller including a first oscillator circuit;
a second microcontroller including a second oscillator circuit; and
at least one of the first microcontroller and the second microcontroller provides for comparing a first frequency of the first oscillator circuit to a second frequency of the second oscillator circuit, and determining a correction factor based on a difference between the first frequency and the second frequency, wherein first microcontroller is selectively actuated to conserve energy, and the second microcontroller selectively actuates the first microcontroller at desired intervals.
1. A method of determining real time in a vehicle comprising the steps of:
a) determining a difference between a frequency of a first crystal oscillator and a second crystal oscillator, wherein the first crystal oscillator is disposed in a first microcontroller and the second crystal oscillator is disposed in a second separate microcontroller; and
b) determining a temperature based on the determined difference between the frequency of the first crystal oscillator and the second crystal oscillator, wherein the difference is determined by comparing an actual difference between the frequency of the first oscillator and the second oscillator to a predetermined difference.
2. The method as recited in
3. The method as recited in
4. The method as recited in
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The application claims priority to U.S. Provisional Application No. 60/708,062 which was filed on Aug. 12, 2005.
This invention generally relates to a method and device for determining real time within a vehicle. More particularly, this invention relates to a method and device for determining real time and temperature within a vehicle.
Many conventional electronic devices require a real time value including time and date. Current devices for keeping and determining the real time include a single relatively large microcontroller that utilizes a crystal oscillator for tracking the passage of time. The large microcontroller requires a relatively large amount of power and is susceptible to power interruptions and aging.
Further, the current devices for keeping track of time require a compensation factor due to temperature variations. The crystal oscillator vibrates or oscillates at a set frequency depending on material and cut. These oscillations vary with temperature and therefore require compensation to remain within a desired level of accuracy. Reduced variation due to temperatures can be obtained by using expensive high precision crystal oscillators. However, such high precision crystal oscillators require considerably more power as compared to a normal crystal oscillator. Many applications require a reduction in power usage to maximize battery life, therefore making the use of such high precision crystal oscillators impractical. The need for an accurate, low power, temperature compensated real time clock still exists.
An example real time clock assembly includes paired crystal oscillators that experience changes in frequency responsive to temperature. The differences in frequency changes between the paired crystal oscillators are utilized to determine temperature.
The example real time clock includes a first microcontroller and a second microcontroller each including a crystal oscillator. Each of the paired crystal oscillators oscillate at different frequencies at different temperatures. The difference in oscillation frequencies is utilized to determine a temperature.
The relationship between frequency and temperature for the pair of crystal oscillators is mapped and stored. During operation, a difference between the frequencies of the paired crystal oscillators is measured. Once a difference between the paired crystal oscillators is detected, a determination is made as to what temperature corresponds to the measured difference in frequencies. Once the temperature is determined, a correction factor is applied to compensate for any drift relating to the determine temperature.
Accordingly, the example device and method utilizes the predictability of frequency responsive to temperature variations by the paired crystal oscillators to provide the determination of temperature in order to determine the applicable correction values or factors.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Referring to
The first microcontroller 12 includes a first oscillator circuit 16 and a first crystal oscillator 20. The crystal oscillator 20 vibrates at a frequency that is utilized to track time as is known. The second microcontroller 14 includes a second oscillator circuit 18 with a second crystal oscillator 22. The first and second crystal oscillators 20, 22 oscillate at different frequencies at different temperatures. The difference in oscillation frequencies is utilized to determine a temperature. The determined temperature is then utilized to apply a compensation value. The example method and assembly determines temperature without the need for a dedicated and separate temperature determination circuit.
Referring to
The difference in frequency change responsive to temperature change is recorded for a plurality of temperatures within a desired range. The differences in frequency between the first crystal oscillator 20 and the second crystal oscillator 22 therefore are paired with a temperature. These paired difference and temperature values are mapped and recorded for use in determining the temperature.
Referring to
Once the relationship between frequency and temperature for the pair of first and second crystal oscillators is determined and mapped, the clock assembly is ready for operation. During operation, a difference between the frequency of the first crystal oscillator 20 and the second crystal oscillator 22 is measured as is indicated by step 40. In most instances, within normal operating temperatures, the difference between frequencies will be small or non-existent. However, as the assembly 10 experiences temperatures outside of the desired operating temperature range, the difference will inevitably increase.
Once a difference between the two frequencies is detected, a determination is made as to what temperature corresponds to the measured difference in frequencies as is indicated at step 42. Once the temperature is determined, a correction factor is applied to compensate for any drift relating to the determine temperature as is indicated at step 44. The method of correcting for the shift of frequency caused by temperature is understood by one skilled in the art.
The predictability of frequency responsive to temperature variations is utilized with the differences in response by the paired crystal oscillators to provide the determination of temperature in order to determine the applicable correction values or factors.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
Desai, Tejas, Farrell, Brian, Costello, John R., King, Douglas J., Chapin, Phillip, Schaffer, Thomas
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Aug 01 2006 | SCHAFFER, THOMAS | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Aug 07 2006 | KING, DOUGLAS J | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Aug 10 2006 | COSTELLO, JOHN R | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Aug 10 2006 | FARRELL, BRIAN | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Aug 11 2006 | Continental Automotive Systems US, Inc. | (assignment on the face of the patent) | / | |||
Aug 11 2006 | CHAPIN, PHIL | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Aug 11 2006 | DESAI, TEJAS | Siemens VDO Automotive Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 018321 | /0184 | |
Dec 03 2007 | Siemens VDO Automotive Corporation | Continental Automotive Systems US, Inc | CHANGE OF NAME SEE DOCUMENT FOR DETAILS | 023050 | /0333 |
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